Title:  Therapeutic using a bispecific antibody

United States Patent:  6,458,933

Issued:  October 1, 2002

Inventors:  Hansen; Hans J. (Morris Plains, NJ)

Assignee:  Immunomedics, Inc. (Morris Plains, NJ)

Appl. No.:  314135

Filed:  May 19, 1999

Multivalent, multispecific molecules having at least one specificity for a pathogen and at least one specificity for the HLA class II invariant chain (Ii) are administered to induce clearance of the pathogen. In addition to pathogens, clearance of therapeutic or diagnostic agents, autoantibodies, anti-graft antibodies, and other undesirable compounds may be induced using the multivalent, multispecific molecules.

DETAILED DESCRIPTION

The invention relates, in general terms, to inducing clearance of a variety of noxious substances from the body. In one aspect of the invention, there is provided a multivalent therapeutic agent, which has at least two different binding specificities. A representative therapeutic agent contains at least one binding specificity for a noxious substance sought to be cleared and at least one specificity to the HLA class II invariant chain (Ii). In another aspect of the invention, there are provided methods of using these therapeutic agents to induce clearance in a patient.

Due to the multiple specificities of the subject therapeutic agents, it is likely that the inventive methods work by forming a bridge between the agent(s) sought to be cleared from the patient and HLA class II molecules. The resulting proximal association, in some manner, is believed to induce or facilitate internalization of the target agent, transportation into lysosomes and degradation of the agent therein.

As used herein "clearance" refers not only to the process of removing the target substance from the body, but also to earlier stages of this process. Clearance also refers to the sequestration of the target substance followed by the removal of the target from, for example, the circulation, lymphatic system, interstitial spaces and the body cavities.

Therapeutic Agents

The therapeutic agents of the invention are multivalent and multispecific. By "multivalent" it is meant that the subject agents may bind more than one target, which may have the same or a different structure, simultaneously. A "target" is either the HLA class II invariant chain or an agent sought to be cleared. By "multispecific" it is meant that the subject agents may bind simultaneously to at least two targets which are of different structure. For example, an agent having one specificity for HLA class II invariant chain and one other specificity for a pathogenic bacterium would be considered multivalent and multispecific because it can bind two structurally different targets simultaneously. On the other hand, a molecule having two specificities for HLA class II invariant chain, but no other specificities, would be multivalent but not multispecific.

Some preferred agents are bispecific, but in some cases additional specificities, e.g. two to six, are preferred. Similarly, some preferred agents are bivalent, but increasing the valency of the agent would be beneficial in binding either additional molecules of the same target or multiple different targets. On preferred class of agents, therefore is bispecific and is at least trivalent, having at least one binding site for Ii and two for the target molecule.

As indicated above, preferred therapeutic agents have at least one specificity directed to HLA class II invariant chain. This specificity confers on the therapeutic agent the characteristic of targeting to invariant chain-positive cells in many organs, such as liver, marrow, spleen, lymph nodes and skin. This targeting is associated with rapid clearance of the therapeutic agent containing this invariant chain specificity through internalization, transport to lysosomes, and subsequent degradation.

The at least one other specificity of the present therapeutic agents may be directed to nearly any substance which it is desirable to have cleared from the body. These substances may be, for example, toxins, pathogenic organisms (e.g., bacteria, fungi, and parasites), viruses, autoantibodies and chemotherapeutic agents. In one embodiment, the pathogenic organism is a fungus of the genus Cryptococcus, and especially Cryptococcus neoformans.

In another embodiment, the pathogenic organism to be cleared is a cancer cell. The cancer cell will be bound to a phagocytic cell expressing HLA class II invariant chain, which may be a macrophage, Kuppfer cell, or histiocyte, for example, with the subsequent destruction of the cancer cell by the phagocytic cell. Although the cancer cell may be internalized by the phagocytic cell, the cancer cell may first be killed by necrotic or apoptoic induction. The tumor-targeting moiety of the multispecific agent may be an antibody reactive with a tumor associated or tumor specific antigen.

Another substance which is desirable to have cleared from the body is an "autoantibody," an antibody that recognizes a native epitope. Autoantibodies may form immune complexes with normal cells or serum components, leading to their damage or clearance by the immune system, just as immune complexes with foreign pathogens. One source of tissue damage is activation of the complement system. Most antibodies, including autoantibodies, have a site on the Fc portion of the immunoglobulin chain that can react with activated C1q or C3 components of the complement system. Complex formation between the autoantibody, activated C1q or C3, and the cellular surface initiates a cascading activation of other complement components, leading to the damage or destruction of the cell to which the autoantibody is bound.

As a result, autoantibodies are responsible for a large number of serious, sometimes life threatening, diseases. Beeson (1994) Am. J. Med. 96:457. For example, autoantibodies may recognize the acetylcholine receptors found in neural muscular junctions, for example. The resulting damage to muscular tissue leads to the development of myasthenia gravis. If the autoantibody is directed to platelets, the resulting platelet destruction can lead to chronic autoimmune thrombocytopenia purpura.

In one embodiment of the present invention, the at least one other specificity of the present therapeutic agent may be directed to the specific binding site of an autoantibody. By directing the other specificity to the specific binding site of the autoantibody, clearance of antibodies with potentially harmful specificities is achieved, while the clearance of useful, normal antibodies is avoided.

In another embodiment, the present therapeutic agent may induce clearance of autoantibodies in the form of an immune complex. In this case, the at least one other specificity of the present therapeutic agent preferably is directed to activated C1q, or activated C3 component, which is bound to the immune complex. Thus, autoantibody clearance may be induced regardless of the epitope recognized by the autoantibody specific binding site. By directing the other specificity only to complement components involved in immune complexes, the clearance and depletion of normal complement components may be avoided. Antibodies that specifically recognize immune complex-bound, activated C1q are described in U.S. Pat. No. 4,595,654, incorporated herein by reference.

Undesirable antibodies may also have specificities against transplanted tissue from other species. For example, porcine organs transplanted into humans typically complex with antibodies present within the human host within hours of transplantation. The host antibodies may activate the complement system, resulting in damage and rejection of the transplanted tissue, Fukushima et al. (1994) Transplantation 57:923; Pruitt et al., (1994) Transplantation 57:363. The major epitope on non-human tissue responsible for transplant rejection is the (.alpha.-galactosyl epitope (Gal.alpha.1-3Gal.beta.1-4GlcNAc-R). Galili et al. (1985) J. Exp. Med. 162:573. Up to 1% of all serum IgG in humans recognizes the .alpha.-galactosyl epitope. Galili et al. (1984) J. Exp. Med. 160:1519.

It is one objective of the invention to ameliorate the rejection response of humans toward non-human tissue by inducing the clearance of antibodies directed toward transplanted tissue. In accord with this objective, the present therapeutic agent has at least one specificity directed to the specific binding site of an anti-graft antibody, and at least one specificity for Ii. In a preferred embodiment, the specific binding site of an anti-graft antibody recognizes the .alpha.-galactosyl epitope. In a more preferred embodiment, the least one specificity for a specific binding site of the anti-graft antibody is a polymer of alpha-galactose.

The chemical constitution of the therapeutic agents may also vary, but they should be capable of specific binding. Accordingly, macromolecule, such as proteins, carbohydrates (e.g., lectins) and RNAs are preferred. Due to the well known ability to generate molecules capable of binding with a wide range of specificities, antibodies and antibody fragments and derivatives are particularly preferred. Both monoclonal and polyclonal antibodies may be prepared according to established methods in the art. Because they bind with a single, defined specificity, monoclonal antibodies are a preferred starting material. Having generated different monoclonal antibodies, and thus a variety different specificities, these starting molecules can be used to generate the multivalent, multispecific agents of the invention. The art is well versed in both recombinant and chemical methods (crosslinking) for generating such agents.

Fragments of antibodies include any portion of the antibody which is capable of binding the target antigen. Antibody fragments specifically include F(ab')₂, Fab, Fab' and Fv fragments. These can be generated from any class of antibody, but typically are made from IgG or IgM. They may be made by conventional recombinant DNA techniques or, using the classical method, by proteolytic digestion with papain or pepsin. See CURRENT PROTOCOLS IN IMMUNOLOGY, chapter 2, Coligan et al., eds., (John Wiley & Sons 1991-92).

F(ab')₂ fragments are typically about 110 kDa (IgG) or about 150 kDa (IgM) and contain two antigen-binding regions, joined at the hinge by disulfide bond(s). Virtually all, if not all, of the Fc is absent in these fragments. Fab' fragments are typically about 55 kDa (IgG) or about 75 kDa (IgM) and can be formed, for example, by reducing the disulfide bond(s) of an F(ab')₂ fragment. The resulting free sulfhydryl group(s) may be used to conveniently conjugate Fab' fragments to other molecules, such as detection reagents (e.g., enzymes).

Fab fragments are monovalent and usually are about 50 kDa (from any source). Fab fragments include the light (L) and heavy (H) chain, variable (V_L and V_H, respectively) and constant (C_L and C_H, respectively) regions of the antigen-binding portion of the antibody. The H and L portions are linked by an intramolecular disulfide bridge.

Fv fragments are typically about 25 kDa (regardless of source) and contain the variable regions of both the light and heavy chains (V_L and V_H, respectively). Usually, the V_L and V_H chains are held together only by non-covalent interacts and, thus, they readily dissociate. They do, however, have the advantage of small size and they retain the same binding properties of the larger Fab fragments. Accordingly, methods have been developed to crosslink the V_L and V_H chains, using, for example, glutaraldehyde (or other chemical crosslinkers), intermolecular disulfide bonds (by incorporation of cysteines) and peptide linkers. The resulting Fv is now a single chain (i.e., SCFv).

One preferred method involves the generation of SCFvs by recombinant methods, which allows the generation of Fvs with new specificities by mixing and matching variable chains from different antibody sources. In a typical method, a recombinant vector would be provided which comprises the appropriate regulatory elements driving expression of a cassette region. The cassette region would contain a DNA encoding a peptide linker, with convenient sites at both the 5' and 3' ends of the linker for generating fusion proteins. The DNA encoding a variable region(s) of interest may be cloned in the vector to form fusion proteins with the linker, thus generating an SCFv.

In an exemplary alternative approach, DNAs encoding two Fvs may be ligated to the DNA encoding the linker, and the resulting tripartite fusion may be ligated directly into a conventional expression vector. The SCFv DNAs generated any of these methods may be expressed in prokaryotic or eukaryotic cells, depending on the vector chosen.

In one embodiment, the agent sought to be cleared is a parasite, such as an leishmania, malaria, trypanosomiasis, babesiosis, or schistosomiasis. In such cases the inventive molecules may be directed against a suitable parasite-associated epitope which includes, but is not limited to, the following.

In another embodiment, the agent sought to be cleared is a virus, such as human immunodeficiency virus (HIV), Epstein-Barr virus (EBV), or hepatitis. In such cases, the inventive therapeutic agent may be directed against a suitable viral epitope including, but not limited to:

The agent sought to be cleared may also be bacterial. In this case, the inventive molecule may have a specificity to a suitable bacterial epitope which includes, but is not limited to:

Pharmaceutical Compositions

Pharmaceutical compositions according to the invention comprise at least one therapeutic agent as described above. In addition, these compositions typically further contain a suitable pharmaceutical excipient. Many such excipients are known to the art and examples may be found in REMINGTON'S PHARMACEUTICAL SCIENCES, chapters 83-92, pages 1519-1714 (Mack Publishing Company 1990) (Remington's), which are hereby incorporated by reference. The choice of excipient will, in general, be determined by compatibility with the therapeutic agent(s) and the route of administration chosen. Although the subject compositions are suitable for administration via numerous routes, parenteral administration is generally preferred. The inventive compositions may be formulated as a unit dose which will contain either a therapeutically effective dose or some fraction thereof.

Methods of Preparing Multivalent Molecules

Multivalent, multispecific antibody derivatives can be prepared by a variety of conventional procedures, ranging from glutaraldehyde linkage to more specific linkages between functional groups. The antibodies and/or antibody fragments are preferably covalently bound to one another, directly or through a linker moiety, through one or more functional groups on the antibody or fragment, e.g., amine, carboxyl, phenyl, thiol, or hydroxyl groups. Various conventional linkers in addition to glutaraldehyde can be used, e.g., disiocyanates, diiosothiocyanates, bis(hydroxysuccinimide) esters, carbodiimides, maleirmidehydroxy-succinimde esters, and the like. The optimal length of the linker may vary according to the type of target cell. The most efficacious linker size can be determined empirically by testing (and ensuring) reactivity to both target and Ii. Such immunochemical techniques are well known.

A simple method to produce multivalent antibodies is to mix the antibodies or fragments in the presence of glutaraldehyde. The initial Schiff base linkages can be stabilized, e.g., by borohydride reduction to secondary amines. A diiosothiocyanate or carbodiimide can be used in place of glutaraldehyde as a non-site-specific linker.

The simplest form of a multivalent, multispecific antibody is a bispecific antibody comprising binding specificities both to a target agent to be cleared and to Ii. Bispecific antibodies can be made by a variety of conventional methods, e.g., disulfide cleavage and reformation of mixtures of whole IgG or, preferably F(ab')₂ fragments, fusions of more than one hybridoma to form polyomas that produce antibodies having more than one specificity, and by genetic engineering. Bispecific antibodies have been prepared by oxidative cleavage of Fab' fragments resulting from reductive cleavage of different antibodies. This is advantageously carried out by mixing two different F(ab')₂ fragments produced by pepsin digestion of two different antibodies, reductive cleavage to form a mixture of Fab' fragments, followed by oxidative reformation of the disulfide linkages to produce a mixture of F(ab')₂ fragments including bispecific antibodies containing a Fab' portion specific to each of the original epitopes (i.e., target and li). General techniques for the preparation of multivalent antibodies may be found, for example, in Nisonhoff et al., Arch Biochem. Biophys. 93: 470 (1961), Hammerling et al., J. Exp. Med. 128: 1461 (1968), and U.S. Pat. No. 4,331,647.

More selective linkage can be achieved by using a heterobifunctional linker such as maleimide-hydroxysuccinimide ester. Reaction of the ester with an antibody or fragment will derivatize amine groups on the antibody or fragment, and the derivative can then be reacted with, e.g., an antibody Fab fragment having free sulfhydryl groups (or, a larger fragment or intact antibody with sulfhydryl groups appended thereto by, e.g., Traut's Reagent). Such a linker is less likely to crosslink groups in the same antibody and improves the selectivity of the linkage.

It is advantageous to link the antibodies or fragments at sites remote from the antigen binding sites. This can be accomplished by, e.g., linkage to cleaved interchain sulfydryl groups, as noted above. Another method involves reacting an antibody having an oxidized carbohydrate portion with another antibody which has at lease one free amine function. This results in an initial Schiff base (imine) linkage, which is preferably stabilized by reduction to a secondary amine, e.g., by borohydride reduction, to form the final product. Such site-specific linkages are disclosed, for small molecules, in U.S. Pat. No. 4,671,958, and for larger addends in U.S. Pat. No. 4,699,784.

The interchain disulfide bridges of the an F(ab')₂ fragment having target specificity are gently reduced with cysteine, taking care to avoid light-heavy chain linkage, to form Fab'-SH fragments. The SH group(s) is(are) activated with an excess of bis-maleimide linker (1,1'-(methylenedi-4,1-phenylene)bis-malemide). An Ii-specific Mab, such as LL1, is converted to Fab'-SH and then reacted with the activated target-specific Fab'-SH fragment to obtain a bispecific antibody.

Alternatively, such bispecific antibodies can be produced by fusing two hybridoma cell lines that produce anti-target Mab and anti-li Mab. Techniques for producing tetradomas are described, for example, by Milstein et al., Nature 305: 537 (1983) and Pohl et al., Int. J. Cancer 54: 418 (1993).

Finally, such bispecific antibodies can be produced by genetic engineering. For example, plasmids containing DNA coding for variable domains of an anti-target Mab can be introduced into hybridomas that secrete LL1 antibodies. The resulting "transfectomas" produce bispecific antibodies that bind target and Ii. Alternatively, chimeric genes can be designed that encode both anti-target and anti-Ii binding domains. General techniques for producing bispecific antibodies by genetic engineering are described, for example, by Songsivilai et al., Biochem. Biophys. Res. Commun. 164: 271 (1989); Traunecker et al., EMBO J. 10: 3655 (1991); and Weiner et al., J. Immunol. 147: 4035 (1991).

A higher order multivalent, multispecific molecule can be obtained by adding various antibody components to a bispecific antibody, produced as above. For example, a bispecific antibody can be reacted with 2-iminothiolane to introduce one or more sulfhydryl groups for use in coupling the bispecific antibody to an further antibody derivative that binds an the same or a different epitope of the target antigen, using the bis-maleimide activation procedure described above. These techniques for producing multivalent antibodies are well known to those of skill in the art. See, for example, U.S. Pat. No. 4,925,648, and Goldenberg, international publication No. WO 92/19273, which are incorporated by reference.

Methods of Treatment

The methods of the invention typically involve administering to a patient in need of treatment a therapeutically effective amount of a composition which comprises a therapeutic agent of the invention. The patient is usually human, but may be a non-human animal. A patient will be in need of treatment where it is desirable to induce clearance of a target agent.

A therapeutically effective amount is generally an amount sufficient to accelerate clearance of the target agent versus a control.

Some methods involve the use of the instant therapeutic agents to induce clearance of cytoreductive agents (chemotherapeutic agents). In a typical method, a patient is treated with a cytoreductive agent, then the excess cytoreductive agent is removed by administration of an inventive compound having at least one specificity for the cytoreductive agent. In one exemplary method, the cytoreductive agent comprises an antibody for targeting and the inventive compound has a specificity for the antibody portion of the agent. In this manner, any portion of the cytoreductive agent that fails to specifically interact with its target is removed. It is anticipated that this method will allow the use of higher, more effective doses of the cytoreductive agent. Side effects will be minimized because the inventive compounds induce clearance of any excess.

Other methods involve reducing the background caused by excess non-localizing diagnostic agents. These methods are useful, for example, in an imaging procedure where a targeting agent (e.g., an antibody) is conjugated with a detectable marker (e.g., a radionuclide). In a typical method, the diagnostic agent would be administered to a patient and, following administration but before detection, an inventive compound having at least one specificity for the diagnostic agent and at least one specificity for Ii is provided to the patient, thereby inducing clearance of the excess diagnostic.

Still other methods involved the clearance of pathogens, such as bacteria, from the patient. It is envisioned that this approach will have particular benefit for patients who have become septic. Typically, these methods involve administering an inventive compound having at least one specificity for a pathogen of interest (e.g., endotoxin) and at least one specificity for Ii, thereby inducing clearance of the pathogen.

The term "treating" in its various grammatical forms in relation to the present invention refers to preventing, curing, reversing, attenuating, alleviating, minimizing, suppressing or halting the deleterious effects of a disease state, disease progression, disease causative agent (e.g., bacteria or viruses) or other abnormal condition. Because some of the inventive methods involve the physical removal of the etiological agent, the artisan will recognize that they are equally effective in situations where the inventive compound is administered prior to, or simultaneous with, exposure to the etiological agent (prophylactic treatment) and situations where the inventive compounds are administered after (even well after) exposure to the etiological agent.

Claim 1 of 13 Claims

What is claimed is:

1. A multivalent molecule having at least one, specificity for a pathogenic organism and at least one specificity for the HLA class II invariant chain (Ii).
 

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